The present invention relates to a method and apparatus for butt-jointing edges of an elastic material sheet made from a sticky material such as uncured rubber.
In a process of manufacturing a pneumatic tire, a strip of uncured rubber in which reinforcing are cords embedded is wound around a drum, and in order to form a cylinder hollow, the circumferential ends of the strip are jointed by simply butting them together utilizing the tackiness of the uncured rubber.
Japanese patent application publication No. 8-238686 discloses an apparatus for jointing the circumferential ends of a wound carcass ply, namely, a strip of uncured rubber in which carcass cords are embedded, wherein as shown in FIG. 19, one pair of conical rotators CR which are rotated at the same speed in the counter directions are pressed against the upper surface of the carcass ply P while supporting the under surface thereof by a cylindrical roller SR. When the edges PE of the ply P pass through the conical rotators CR, the upper surfaces of the edge portions are drawn towards the center Gc by the conical surfaces of the conical rotators CR, and the edges are butt-jointed.
In order to butt-joint the edges strongly and surely, if the force to draw the upper surfaces of the edge portions is increased, then the edge portions are liable to crinkle and the joint is liable to stagger. This is remarkable when the cords embedded are organic fiber cords softer than steel cords. If the force to draw is small, during building the raw tire for example, the joint is broken and the tire uniformity such as Radial force variation is deteriorated.